researching United flight 940 from LAX through ORD to FRA, Flight Tracker is only tracking the ORD to FRA leg. Flight Tracker problem 
It’s a flight number issue… I noticed the same thing with UAL932 - It’s supposed to be DEN-IAD-FRA, but the DEN-IAD leg is scheduled as UAL8132…
It’s not a FlightAware problem, United just dispatches the flight as something other than UAL940 for the LAX-ORD leg. You just have to do some of the work to figure out which flight it should be. (In this case looks like it’s UAL940K - http://flightaware.com/live/flight/UAL940K) 
thanks